1. Field of the Invention
The present invention relates to an ozone beam generation apparatus and a method for generating an ozone beam and particularly to an apparatus and a method which permits the precise and steady supply of pure ozone as a strong oxidizing agent during oxidation processes performed under vacuum, such as the formation of high temperature-superconductive thin films, silicon oxide films, and insulating films in the production of semiconductor devices.
2. Description of the Prior Art
An oxidation treatment under vacuum has been performed according to a variety of techniques such as plasma processing, high temperature treatment in an oxygen atmosphere, a method in which active oxygen is supplied by an ion gun, or a method in which an ozonizer is directly connected to a processing apparatus to introduce ozonized oxygen into the processing apparatus. However, these methods suffer from various problems such as insufficient oxidizing capacity, formation of defects in the treated substances during high temperature treatments and physical sputtering processes, and formation of non-uniform products.
FIG. 1 shows an embodiment of the conventional ozone beam generation apparatus. This is an apparatus for supplying ozone to a processing chamber 1 in which a sample 2 is oxidized. An ozone-containing gas generated in an ozonizer 6 is fed to an ozone chamber 5 of quartz glass accommodated in a liquid nitrogen reservoir 4 through a valve 7, and the chamber 5 is evacuated by an operating vacuum pump 3 to establish a low pressure within the chamber. The pressure in the chamber 5 is measured with a vacuum gauge 8. To thereby liquefy only ozone present within chamber 5, valves 7 and 12 are closed at a time when a desired amount of ozone is liquefied. Then a valve 13, positioned between the ozone chamber 5 and the chamber, 1 which has been previously evacuated by a vacuum pump 15, is opened followed by the operation of a temperature control device 9 and the heating of the ozone chamber 5 by a heater 10 in order to gasify the liquefied ozone. The temperature of the ozone chamber 5 is determined by a thermo-couple 11 and is held at a predetermined level by the temperature control device. The gasified ozone is supplied to the sample 2 through a pipe 14. In such a conventional ozone beam generation apparatus in which liquid nitrogen is employed, it is impossible to precisely perform temperature control, which in turn leads to difficult control of the ozone dose, contamination of ozone with oxygen during liquefaction thereof and a high possibility of explosion.
To precisely control the ozone dose and to eliminate the possibility of explosion, the following problems must be solved:
(1) Liquefaction or solidification of pure ozone: It is necessary to steadily liquefy or solidify only ozone in the gas supplied from an ozonizer and simultaneously prevent the contamination thereof with impurities which can exert catalytic action on the ozone.
(2) Precise control of the saturated vapor pressure of ozone: The saturated vapor pressure of ozone is a function of temperature and, therefore, the temperature of ozone must precisely be controlled within an accuracy of 0.1K in order to precisely control the dose of ozone.
(3) Safety measures against ozone explosion: Ozone is an unstable substance. For this reason, it must not only be handled within a low temperature and pressure atmosphere, but also be kept away from contamination with impurities which may trigger explosion, and irradiation with ultraviolet rays as much as possible. Moreover, the materials for containers which come in contact with pure ozone gas, liquified ozone or solidified ozone must be those which do not serve as a catalyst for ozone. In addition, safety measures must be taken so that human bodies and the apparatuses can certainly be protected against damages even if explosion accidentally takes place.